Question

我想开发一个

的应用程序

在外部存储中创建文件

2.只要点击开始按钮，就可以将加速度计读数写入文件

3.单击停止按钮时停止写入

4.单击阅读按钮

我不知道如何在外部存储中创建文件并将加速度计的读数存储在其中，然后从文件中读取值。

我在MainACtivity.java中尝试了以下代码

package com.example.startstopbuttonaccelerometerreading;

import java.io.File;
import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.io.OutputStreamWriter;

import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.app.Activity;
import android.content.Context;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.RelativeLayout;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity implements SensorEventListener {

private SensorManager mSensorManager;
private Sensor mAccelerometer;
TextView title,tv,tv1,tv2;
RelativeLayout layout;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    mSensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
    mAccelerometer = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
  //get layout
    layout = (RelativeLayout) findViewById(R.id.relative);

    //get textviews
    title=(TextView)findViewById(R.id.name);   
    tv=(TextView)findViewById(R.id.xval);
    tv1=(TextView)findViewById(R.id.yval);
    tv2=(TextView)findViewById(R.id.zval);

    }


public void onStartClick(View view) {
    final SensorEventListener mySensorEventListener = new SensorEventListener() { 
        public void onSensorChanged(SensorEvent sensorEvent) {
        if (sensorEvent.sensor.getType() == Sensor.TYPE_ACCELEROMETER) {


        float x = sensorEvent.values[0]; 
        float y = sensorEvent.values[1]; 
        float z = sensorEvent.values[2]; // TODO apply the acceleration changes to your application.
        textView.append("\nACC_x = "+ x + ", ACC_y = "+y+ ", ACC_z = " + z);
        acc+="\n"+x+ ", "+ y+","+z;

        try {
            File myFile = new File("/sdcard/acc.txt");
            myFile.createNewFile();
            FileOutputStream fOut = new FileOutputStream(myFile);
            OutputStreamWriter myOutWriter = 
                                    new OutputStreamWriter(fOut);
            myOutWriter.append(acc);
            myOutWriter.close();
            fOut.close();
            Toast.makeText(getBaseContext(),
                    "Done writing SD 'acc.txt'",
                    Toast.LENGTH_SHORT).show();
        } catch (Exception e) {
            Toast.makeText(getBaseContext(), e.getMessage(),
                    Toast.LENGTH_SHORT).show();
        }

        }
    }
        @Override
        public void onAccuracyChanged(Sensor sensor, int accuracy) {
            // TODO Auto-generated method stub

        }
    };
    // write on SD card file data in the text box 
    int sensorType = Sensor.TYPE_ACCELEROMETER; 
    mSensorManager.registerListener(this, mAccelerometer, SensorManager.SENSOR_DELAY_NORMAL);

}// onClick
;


public void onStopClick(View view) {
    mSensorManager.unregisterListener(this);
}


@Override
public void onAccuracyChanged(Sensor sensor, int accuracy) {

}



}

这是activity_main.xml代码：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity"
    android:id="@+id/relative" >

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="40dp"
        android:layout_marginTop="124dp"
        android:text="Start"
        android:onClick="onStartClick" />

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBottom="@+id/button1"
        android:layout_marginLeft="37dp"
        android:layout_toRightOf="@+id/button1"
        android:text="Stop"
        android:onClick="onStopClick" />
    <TextView
    android:textSize="30dp"
    android:id="@+id/name"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    />

   <TextView
    android:textSize="20dp"
    android:layout_below="@+id/name"
    android:id="@+id/xval"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    />

    <TextView
    android:textSize="20dp"
    android:id="@+id/yval"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_below="@+id/xval"
    />

    <TextView
    android:textSize="20dp"
    android:id="@+id/zval"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_below="@+id/yval"
    />

</RelativeLayout>

我在androidmanifest.xml中写了权限

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

MainActivity未编译。错误是acc，textview无法解决。我想知道在外部存储器中创建文件的代码，并向其写入加速度计读数并从文件中读取数据。

Answer 1

我已将您的代码重写为以下内容，包括AndroidManifest.xml，activity_main.xml和MainActivity.java。

此程序中有三个按钮。

1.开始：开始将三轴数据写入acc.txt。

2.停止：停止写数据。

3.阅读：阅读acc.txt中的所有数据

我创建了一个编辑文本，在单击“读取”按钮后显示acc.txt中的内容。这个程序有一些延迟时间。你可以自己调整它。

<强>的AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.so_problem"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/> 

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="18" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.example.so_problem.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

<强> activity_main.xml中

    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:paddingBottom="@dimen/activity_vertical_margin"
        android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity"
    android:id="@+id/relative" >

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="40dp"
        android:layout_marginTop="124dp"
        android:text="Start"
        android:onClick="onStartClick" />

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBottom="@+id/button1"
        android:layout_marginLeft="37dp"
        android:layout_toRightOf="@+id/button1"
        android:text="Stop"
        android:onClick="onStopClick" />

     <Button
        android:id="@+id/button3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/button1"
        android:layout_alignRight="@+id/button2"
        android:layout_centerVertical="true"
        android:text="Read"
        android:onClick="onReadClick" />

    <TextView
        android:id="@+id/name"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:textSize="30dp" />

   <TextView
        android:textSize="20dp"
        android:layout_below="@+id/name"
        android:id="@+id/xval"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content" />

    <TextView
        android:textSize="20dp"
        android:id="@+id/yval"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/xval" />

    <TextView
        android:textSize="20dp"
    android:id="@+id/zval"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/yval" />

    <EditText
        android:id="@+id/showval"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/zval"
        android:layout_alignRight="@+id/zval"
        android:layout_below="@+id/button3"
        android:layout_marginTop="18dp"
        android:clickable="false"
        android:cursorVisible="false"
        android:editable="false"
        android:ems="10"
        android:freezesText="true"
        android:inputType="none"
        android:lines="8"
        android:maxLines="1000"
        android:scrollbars="vertical"
        android:singleLine="false" />

</RelativeLayout>

<强> MainActivity.java

package com.example.so_problem;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

import android.app.Activity;
import android.content.Context;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.os.Handler;
import android.os.HandlerThread;
import android.os.Message;
import android.util.Log;
import android.view.View;
import android.widget.EditText;
import android.widget.RelativeLayout;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity implements SensorEventListener 
{

    private SensorManager mSensorManager;
    private Sensor mAccelerometer;
    TextView title,tvx,tvy,tvz;
    EditText etshowval;
    RelativeLayout layout;
    private String acc;
    private String read_str = "";
    private final String filepath = "/mnt/sdcard/acc.txt";
    private BufferedWriter mBufferedWriter;
    private BufferedReader mBufferedReader;
    private float x;
    private float y;
    private float z;

    public static final int MSG_DONE = 1;
    public static final int MSG_ERROR = 2;
    public static final int MSG_STOP = 3;

    private boolean mrunning;
    private Handler mHandler;
    private HandlerThread mHandlerThread;

    private Handler uiHandler = new Handler(){
        public void handleMessage(Message msg){ 
            String str = (String) msg.obj;
            switch (msg.what)
            {
                case MSG_DONE:
                    Toast.makeText(getBaseContext(), str,
                            Toast.LENGTH_SHORT).show();
                    break;
                case MSG_ERROR: 
                    Toast.makeText(getBaseContext(),str,
                            Toast.LENGTH_SHORT).show();
                    break;
                case MSG_STOP:
                    Toast.makeText(getBaseContext(), str,
                            Toast.LENGTH_SHORT).show();
                default:
                    break;
            }
            super.handleMessage(msg);
        }
    };

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mSensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
        mAccelerometer = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
        mSensorManager.registerListener(this, mAccelerometer, SensorManager.SENSOR_DELAY_NORMAL);
      //get layout
        layout = (RelativeLayout) findViewById(R.id.relative);

        //get textviews
        title = (TextView)findViewById(R.id.name);   
        tvx = (TextView)findViewById(R.id.xval);
        tvy = (TextView)findViewById(R.id.yval);
        tvz = (TextView)findViewById(R.id.zval);
        etshowval = (EditText)findViewById(R.id.showval);
        title.setText("Accelerator");

        mHandlerThread = new HandlerThread("Working Thread");
        mHandlerThread.start();

        mHandler = new Handler(mHandlerThread.getLooper());
        mHandler.post(r);
    }

    private Runnable r = new Runnable(){
        @Override
        public void run ()
        {
            while(true)
            {
                if (mrunning)
                {
                    Message msg1 = new Message();
                    try 
                    {
                        WriteFile(filepath,acc);
                        msg1.what = MSG_DONE;
                        msg1.obj = "Start to write to SD 'acc.txt'";
                    } 
                    catch (Exception e) 
                    {
                        msg1.what = MSG_ERROR;
                        msg1.obj = e.getMessage();
                    }
                    uiHandler.sendMessage(msg1);
                }
                else
                {   
                    Message msg2 = new Message();
                    msg2.what = MSG_STOP;
                    msg2.obj = "Stop to write to SD 'acc.txt'";
                    uiHandler.sendMessage(msg2);
                }

                try {
                    Thread.sleep(500);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }
    };

    public void onStartClick(View view) 
    {
        start();
    }

    public void onStopClick(View view) 
    {
        stop();
    }

    public void onReadClick(View view) 
    {
        etshowval.setText(ReadFile(filepath));
    }

    private synchronized void start()
    {
        mrunning = true;
    }

    private synchronized void stop()
    {
        mrunning = false;
    }

    @Override
    public void onAccuracyChanged(Sensor sensor, int accuracy) 
    {
    }

    @Override
    public void onSensorChanged(SensorEvent sensorEvent) 
    {
        // TODO Auto-generated method stub

        if (sensorEvent.sensor.getType() == Sensor.TYPE_ACCELEROMETER) 
        {
            x = sensorEvent.values[0]; 
            y = sensorEvent.values[1]; 
            z = sensorEvent.values[2]; 
            acc= String.valueOf(x) + ", " + String.valueOf(y) + ", " + String.valueOf(z);

            tvx.setText("X = "+ String.valueOf(x));
            tvy.setText("Y = "+ String.valueOf(y));
            tvz.setText("Z = "+ String.valueOf(z));
        }
    }

    public void CreateFile(String path)
    {
        File f = new File(path);
        try {
            Log.d("ACTIVITY", "Create a File.");
            f.createNewFile();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    public String ReadFile (String filepath)
    {
        mBufferedReader = null;
        String tmp = null;

        if (!FileIsExist(filepath))
            CreateFile(filepath);

        try 
        {
            mBufferedReader = new BufferedReader(new FileReader(filepath));
            // Read string
            while ((tmp = mBufferedReader.readLine()) != null) 
            {
                tmp += "\n";
                read_str += tmp;
            }
        } 
        catch (IOException e) 
        {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return read_str;
    }

    public void WriteFile(String filepath, String str)
    {
        mBufferedWriter = null;

        if (!FileIsExist(filepath))
            CreateFile(filepath);

        try 
        {
            mBufferedWriter = new BufferedWriter(new FileWriter(filepath, true));
            mBufferedWriter.write(str);
            mBufferedWriter.newLine();
            mBufferedWriter.flush();
            mBufferedWriter.close();
        }
        catch (IOException e) 
        {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    public boolean FileIsExist(String filepath)
    {
        File f = new File(filepath);

        if (! f.exists())
        {
            Log.e("ACTIVITY", "File does not exist.");
            return false;
        }
        else
            return true;
    }

    @Override
    protected void onPause()
    {
    // TODO Auto-generated method stub
        mSensorManager.unregisterListener(this);
        Toast.makeText(this, "Unregister accelerometerListener", Toast.LENGTH_LONG).show();
        super.onPause();
    } 
}

Answer 2

 textView.append("\nACC_x = "+ x + ", ACC_y = "+y+ ", ACC_z = " + z);
acc+="\n"+x+ ", "+ y+","+z;

您没有在任何地方声明“textView”或“acc”变量

即使在解决了这个问题之后，上面提供的代码示例也会以仅包含最新传感器事件记录的文件结束。因为每次传感器事件发生时它都会创建一个新文件，将测量值写入其中，并关闭它。当传递新测量时，将使用相同的名称创建新文件，因此将删除旧条目。

执行该任务的良好做法可能如下：

将文件流存储为活动中的私有变量
在开始按钮的单击事件处理程序中，打开文件或创建文件（如果不存在）并将其流存储到活动的私有变量中。还要将侦听器注册到加速计传感器事件。
在onSensorChanged事件中，将新测量值附加到文件流
在停止按钮的点击事件处理程序中，取消注册lisetener，然后关闭文件流。

存储加速度计值

2 个答案: